Cassini's mission is drawing to an end, as NASA prepares to crash it into the surface of Saturn itself. But the craft has, this week, sent back a beautiful new picture of the Earth, glimpsed through Saturn's rings.

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Saturn's moons Enceladus and Titan are believed to be geologically active - and could even support life thanks to vast subsurface oceans. That's part of the reason that NASA wants to avoid crashing Cassini into either of them.

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Since arriving at Saturn (it travels at 2,040m/s), the 6.8-meter high spacecraft has collected huge amounts of data and snapped many pictures of one of the most fascinating planets in the solar system.

What has Cassini discovered?

In 2013, Cassini captured high resolution images of Saturn lit up by the sun.

Analysis of the samples collected revealed that there was hydrogen gas present in the water that exists under the icy surface.

The presence of hydrogen in the moon's ocean means that microbes (if any exist there) could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in the water.

This chemical reaction, known as "methanogenesis" because it produces methane as a byproduct, is at the root of the tree of life on Earth, and could even have been critical to the origin of life on our planet.

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It's not conclusive proof of alien life - but the discovery is helping evolve our understanding of Enceladus.

"This is the closest we've come, so far, to identifying a place with some of the ingredients needed for a habitable environment," said Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate at Headquarters in Washington.

"These results demonstrate the interconnected nature of NASA's science missions that are getting us closer to answering whether we are indeed alone or not."

When - and how - will Cassini die?

Cassini operates too far from the sun to be powered by solar panels. Instead, it draws its power from radioisotope thermoelectric generator (RTG). This is, in effect, a small lump of decaying plutonium-238 that gives off heat and power as it breaks down.

Although the RTG will still have power when Cassini terminates, it won't have enough to power any further orbits of the massive planet.